Tuberculosis is the number one cause of death due to a bacterial pathogen. There is a fundamental gap in understanding how Mycobacterium tuberculosis subverts macrophage defense functions in order to persistently infect the human host. The long term goal is to reveal the mechanisms employed by M. tuberculosis bacilli to manipulate macrophage-mediated host defenses. The objective of this particular application is to determine the mechanisms by which the macrophage scavenger receptor MARCO participates in M. tuberculosis infection, since single nucleotide polymorphisms in the MARCO gene render the host more susceptible or resistant to tuberculosis. The central hypothesis is that binding of MARCO by the M. tuberculosis cell wall glycolipid, trehalose dimycolate, is important in the macrophage response to infection. The rationale for the proposed research is that understanding how MARCO drives susceptibility or resistance to infection will enable intervention strategies to be developed that will interfere with this process. Thus, the proposed research is relevant to that part of NIH's mission that pertains to developing fundamental knowledge that will potentially help to reduce the burdens of human disease. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: Specific Aim 1: Determine the mechanism(s) for the MARCO SNP associated with susceptibility to TB. Specific Aim 2: Determine the mechanism(s) for the MARCO SNP associated with resistance to TB. Under the first aim, an already proven transfection approach, using MARCO deletion constructs, will be used to test binding, uptake, and downstream responses to TDM-coated particles and M. tuberculosis. Constructs and antibodies that are already on hand will be used. Under the second aim, human peripheral blood monocytes with or without the single nucleotide polymorphism associated with resistance to tuberculosis will be tested for expression, regulatory activity, and survival of M. tuberculosis. Upon completion of the proposed study, we expect to have a better understanding of how MARCO interacts with TDM and M. tuberculosis and how this interaction drives either susceptibility or resistance to tuberculosis. The proposed approach is innovative, because it focuses on a host cell pathway rather than focusing on the development of antibacterial drugs, which is the status quo. The proposed research is significant because it is expected to offer targets for drug therapies, which will enhance the ability of the innate immune system to effectively eliminate M. tuberculosis infection. PUBLIC HEALTH RELEVANCE: The proposed research has relevance to public health because the fundamental mechanisms of the MARCO-M. tuberculosis interaction and its consequences can then be used to manipulate the course of infection. Thus, the findings are expected to provide new targets for developing alternative therapies for tuberculosis in human beings.